Manufacture of nondetonating fuses for blasting and similar purposes



Nov. 28, 1944. w. A CALDWELL ETAL 2,363,559

MANUFACTURE OF NONDETONATING FUSES FOR BLASTING AND SIMILAR PURPOSES' Filed April 30. 1941 rfaM fl., ...L/a. I

Patented Nov. 28, 1944 y UNITED STATES PATENT OFFICE MANUFACTURE F NONDETONATING FUSES FOR BLASTING AND SIMILAR PURPOSES Walter Anderson Caldwell, West Kilbride, and Albert Greville White, Saltcoats, Scotland, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain Application April 30, 1941, Serial No. 391,206

In Great Britain July 1, 1940 13 Claims.

striking at an unregulated speed through the whole length of the material of the core, and the core is forced to burn at a predetermined rate along its length.

In the manufacture of safety fuse, for instance, a core of fuse powder is enveloped in a textile sheath which may be spun directly round a stream of the powder or round tape caused to envelop the powder stream, and the resulting cord is usually passed through a die to ensure that so far as possible the central channel shall be packed with fuse powder whereby the burning speed of the fuse may be rendered serviceably regular. Further coverings may then be applied. For many applications it is necessary to protect the core from the access of moisture, and this is achieved by the application of bitumen, guttapercha or the like waterproofing compositions to the exterior of the textile sheath. Particular care has to be taken in waterproofing the safety fuse since any aw may result in the introduction of Water along the core of the fuse from the exterior at the awed place with consequent failure of the fuse. While the careful application of waterproong composition to the exterior of the textile sheath sufilciently protects the core from the direct access of moisture across the sheath, if the unprotected end of the fuse is allowed to become wet, the moisture is liable t0 creep along the core and render the fuse unserviceable. The present invention provides non- I detonating fuse having a core which is so little properties, oi a polyhydroxy compound is formed into a continuous imperforate core and prevented from burning along its continuous surface by an envelope of less combustible or incombustible material.

According to a further feature of our invention,

the burning speed may be modified, and the development of irregularities in burning speed as a result of mechanical breakage of the core may be avoided, by the embedding longitudinally in the material of the core of a metal filament. This may conveniently be made of a soft conducting metal or alloy such as copper. brass, aluminium, tin, German silver, bronze, phosphor-bronze or the like, or alloys of lead and tin such as those suitable for solder. The metal filament may advantageously be of 30 to 40 standard wire gauge thickness `(0.0124 to 0.0048 inch). Filaments of textile or synthetic material may also be longitudinally embedded in the core. The inclusion of the filaments is conveniently effected by leading them through the nozzle of the extrusion device from which the core is being extruded.

The core of the coherent imperforate composition may advantageously be formed by extrusion,

if desired from a composition made with the assistance of volatile ingredients which are subsequently removed before the envelope is applied'. The extrusion may be carried out at ordinary or increased temperature. The envelope in immediate contact with the core may advantageously take the form of a textile or paper covering pressed into close contact with the core, or a continuous adherent coating comprising a plastic lm forming material. Further coverings may be applied thereover.

4o may include for instance oxidisable metals and metallic alloys, non-metallic elements, silicides, charcoal and the like. The organic polynitrate may consistior instance of a nitrated carbohydrate such as nitrocellulose, nitrostarch or nitrodextrine, but other gelatinisable polynitrates of poly-hydric alcohols may be employed, for instance polyvinyl nitrate. The organic polynitrate may be gelatinised with volatile or nonvolatile solvents, or both, and if volatile ingredients are employed these are substantially evaporated away before the continuous coherent coating is applied.

It the protective envelope in Aimmediate contact with the core is to be made from yarn or strip material it may be spun, twisted or curled round the core as the latter is advanced from the extrusion apparatus, and the enveloped core is drawn through a die so as to ensure a close contact.

lne protective envelope may consist of a plastic lm forming material less combustible than the coherent imperforate core; and if the fuseis intended to be used in circumstances where anypart of the fuse may be subjected to sharp fiexure and to overheating from without, the material of the protective envelope in immediate contact with the core must either be of an infusible nature or if it is fusible must consist of material that will not ow sufliciently to occupy any fortuitous cracks or breaks in the core before the self-ignition temperature of the core material is attained' as the burning of the core'v progresses along the fuse. Thus materials such as glue, gelatine, casein and other protein substances; infusible or difficultly fusible synthetic resins, infusible or diicultly fusible synthetic cellulose derivatives suchas ethyl cellulose, cellulose acetate, glycol cellulose, methyl cellulosa-or salts of cellulose glycolic acid; infusible carbo-hydrates such as dextrin, agar agar, al-

, ginates; or gum arabic; or oxidised oils 'or vulcanised rubber or neoprene may be used.

On the other hand if the fuse is not intended for use under such circumstances more easily thermoplastic materials or fusible materials can be used, such as asphalt,4 tars, pitches, bitumens,

various waxes and thermoplastic or fusible resins,

natural or synthetic rubber-like materials both natural and artificial such as gutta-percha-and balata. Appropriate softening agents 'or other effect materials for instance reproong agents,

waterproofing agents and llers may if desired be included in the composition applied to the coherent imperforate column of combustible material. The coating may, if desired, be applied with the aid of a volatile solvent and it may be applied by dipping, brushing, drawing, spraying, extrusion or otherwise at ordinary or increased temperatures. When a volatile solvent is used the coating may be dried off at suitably raisedtemperature. vIn any case the coating must withstand storage at ordinary hot storage temperatures without appreciable distortion. y

If the envelope or one of the coverings in close proximity to the core is water permeable we prefer to surround it with a waterproof cover which may be of fusible material such as bitumen.

In the accompanying drawing' there is illustrated an apparatus suitable for the manufacture of the coherent imperforate core with the central Wire embedded therein. Referring to the drawing a tube I has housed within it a worm 2 designed to force plastic material in the tube l up into the space 3. The tube l is jacketed at 4 so that the material can be heated in the course of its journey up the tube I. The space 3 is also jacketed at 5 so that the temperature of the material can be maintained when in the space 3. The space 3 narrows to a nozzle 6 through which the material which is being introduced through the tube l is extruded. In alignment with the extrusion nozzle 6 is a guide 'l which carries the central wire 8, the end of the guide 'l being a close t round wire 8 so that none of the material is forced back through the guide.

In operation the material which is to be made into the imperforate coherent core is fed into the tube l in the form of a paste. consistency is obtained'through the presence of a solvent, extrusion can usually be carried out at room temperatures in which case the heating jackets 4 and 5 can be dispensed with. If, however, the material of the core is a thermoplastic If this paste-like material it is essential to maintain the tempera'- ture of the space 3 above the softening point of the core material.- Before any of the material has' been carried by the worm 2 into the space 3 the centre wire 8 is threaded through the guide l so that its4 end passes right out of the nozzle 6. In the course of time the worm 2 forces so much of the core material into space 3 that it commences to extrude round the wire 8 in the form of a thin rod. When this occurs the end of the wire 8 is drawn away so that it moves through the Inozzle S at exactly the same rate as the core material is being extruded. This results in a long coherent imperforate rod of the `core material being made which has embedded within it a soft metal wire. This rod can then be passed into a bath in which it is coated with the chosen coating composition and further layers can be added if desired.

To make a core which has no centre wire, similar apparatus can be used omitting the guide 1.

The invention is further illustrated by the following examples.

Example l 40 parts of a mixture made by grinding together 70% of potassium nitrate and 30% of charcoal are added toa syrup formed by mixing 9 parts of low viscosity nitrocellulose with 14 parts of a liquid mixture of dinitro-toluene isomers at 100 C. The whole is compounded into a paste in a. Werner Pfleiderer mixer maintained at a temperature ofA 100 C. The paste is then transferred to an extrusion apparatus which is also kept heated to 100 C. and extruded into the form of a rod'about one twentieth of aninch in diameter. The rod solidies immediately on cooling and is drawn through a bath of liquid glue and dried oil. A protective coating of textile material is then spun round the rod.

By applying a layer of bitumen or gutta-percha round the textile material a safety fuseof excellent resistance to moisture can be made. Further coats can be added if desired. Y

Example II The procedure is as in Example I except that a 36 gauge S. W. G. copper wire is led centrally ,through the extrusion nozzle at the same rate as the plastic is extruded from it. The burning speed of the safety fuse so obtained is faster than that of the fuse prepared according to Example I.

Example III .extruded into the form of a rod about one twentieth of an inch in diameter, which solidies immediately on cooling, and is drawn through a bath of liquid glue and dried. A protective covering of textile material is then spun around the rod which forms a safety fuse with a good resistance to moisture. Further coats can be put on if desired.

Example IV 52 parts of trirplumbic tetroxide are vpassed through a' 200 mesh sieve. 22 parts of calcium silicide are likewise passed through a 200 mesh sieve and then mixed with the sieved triplumbic tetroxide. A syrup is then made by mixing 17 parts of nitrocellulose with 23 parts of liquid dinitrotoluene isomers at 100 C. and the triplumbic tetroxide-calcium silicide mixture added to it. This is compounded to a smooth paste in a Werner Pileiderer mixer at 100 C. and transferred to an extruding press also kept at 100 C. and extruded into the form of a rod about one twentieth of an inch thickness which sets immediately on cooling. This is then passed through a bath containing an acetone solution of an industrial nitrocellulose containing 30% by weight of tricresylphosphate. The acetone is then permitted to evaporate and the fuse so formed is given a protective textile covering. 'Ihe fuse so formed has an excellent resistance to moisture.

Fuses made according to the above examples can be used with safety in mining and also in circumstances where the fuse is liable to be subjected both to sharp exing and high temperature.

Example V 54 parts of potassium nitrate are ground together with 23 parts of charcoal and theresulting mixture is added' to 23 parts of industrial nitrocellulose dissolved in acetone and worked up into a :paste in a Werner Pfleiderer mixer. The paste is then put into an extrusion press and extruded in the form' of a long rod about one twentieth of an inch thickness. The acetone is allowed to evaporate from this rod, a process taking from 24 to 48y hours, and the rod is then drawn through a bath of molten bitumen and the bitumen coating is allowed to cool. A protective textile layer is then woven around the coated rod which forms a steadily burning safety fuse with a very much higher resistance to moisture than an ordinary black :powder safety fuse, but should only be used in circumstances in which it, will not be exposed to an exterior temperature sufcient to melt the Ibitumen unless care is taken that the fuse is never bent and so never develops any cracks in the core.

This invention isa valuable advance in the art as by its use there can be provided a fuse core which is inherently waterproof such as that of Example IV. Even when using the fuse core mix- I ture of Example I,` which includes a water soluble salt, we have immersed the core material, without any coverings in water for an hour, and found that it win sun bum immediately after removal from the water. In ordinary mixing practice resistance to water of this latter order is sufllcient, to prevent water from creeping along the core of a fuse to render it unserviceable, even though a break has occurred in the outer waterproofing or the end of the fuse has been allowed to fall into water.

As many apparently widely different embodiments of the invention will be apparent without departing from the spirit and scope thereof, it must be understood that the invention is not limited to any specic embodiment except as defined in the appended claims.

p We claim:

l. A method of manufacturing a fuse which comprises extruding into a coherent imperforate core about a soft wire a deflagrating mixture of normally pulverulent oxidising and reducing agents bonded together by means of not, more vthan about its own weight of a non-volatile nondetonating binding agent comprising a gelatinised polynitrate, characterised by colloidal properties, of an organic polyhydroxy compound, said binding agent being present in sulcient quantity to occupy completely the voids between the normally pulverulent material and to provide a voidless core, applying to the core `a coating of lm- 'forming material, spinning a continuous textile gether by means of not more than about its own weight of a non-volatile, non-detonating binding agent comprising a gelatinised polynitrate, char-- acterized by colloidal properties, of an organic polyhydroxy compound, said binding agent being present in s uicient quantity to occupy completely the voids between the normally pulverulent material and to provide a voidless core, simultaneously delivering a soft metal wire centrally through the orifice within the core, applying to the core a coating of nlm-forming material, spinning a continuous textile covering over the coating, and applying a further coating of 'fusible waterproof material, the several coatings being continuously formed ofrelatively incombustible material and of suicient thickness to prevent the core from burning along its outer surface.

3. A rfuse comprising a coherent substantially voidless combustible core, which core comprises a. mixture of pulverulent oxidising and reducing agents, and an amount, not greater than the weight of said mixture, of a non-volatile nondetonating binding agent comprising a gelatinized polynitrate of colloidal character suflicient in proportion to ll the spaces normally existing between said pulverulent agents and provide a voidless core; and a substantially continuous envelospe on said core, of material which is at least less readily combustible than said core, to prevent the core from burning along its outer surface.

4. A fuse comprising a coherent substantially voidless combustible core, which core comprises a mixture of pulverulent oxidising and reducing agents in major proportion by Weight and a minor proportiony of a non-volatilenon-detonating binding agent comprising a gelatinized polynitrate of colloidal character sufficient in proportion to ll the spaces normally existing between said lpulverulent agents and provide a voidless core, a soft metal wire embedded in and surrounded by said core, and an envelope of relatively incombustible or completely incombustible material on said core, to prevent the core from burning along its outer surface. A

5. The fuse of claim 3 wherein the gelatinized polynitra'te is a nitrated carbohydrate.v

6. The fuse of claim 3 wherein thegelatinized polynitrate is nitrocellulose.

7. A fuse comprising a coherent substantially voidless combustible core, which core comprises a. mixture of pulverulent oxidising and reducing agents, and an amount not greater than the weight of said mixture, of a non-volatile nondetonating lbinding agent comprising a gelatinized polynitrate of colloidal character suflicie'nt in proportion to flll the spaces normally existing between said pulverulent agents and provide a voidless core; and an envelope of relatively incombustible or completely incombustifble material on said core, of sufficiently high flowing temperature that; at any given point along the fuse it remains suciently solid as not to ow into cracks or breaks in said core before the self-ignition temperature of the core is attained at such fpoint, said envelope being continuous and of sufcient thickness to prevent the core from burning on its outer surface.

8. The fuse of laim 7 wherein the envelope is of infusible material.

9. The fuse of claim 3 wherein the envelope comprises a protein, a dicultly fusible resin, an

infusible carbohydrate and vulcanized rubber or vulcanized rubber-like material.

10. Therfuse of claim 3 wherein at least the outer portion of said envelope is of waterproof material.

11. Thefuse of claim 3, wherein the binding agent consists of a. polynitrate and a. non-volatile solvent as gelatinizer.

12. The fuse of claim 3, wherein the gelatinized polynitrate is nitrocellulose and liquid dinitrotoluene isomers. v

13. The fuse of claim 3, wherein the inner portion of the-envelope is of glue.

WALTER. ANDERSON CALDWELL. ALBERT GREVIILE WHITE. 

